Iris lends colour to it (7)
I believe the answer is:
eyeball
'iris' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for eyeball that I've seen before include "Optic organ" , "Observe closely" , "" - to - " = in close confrontation" , "Look at closely" , "Ocular orb" .)